Defects in MYOT are the cause of limb-girdle muscular dystrophy type 1A (LGMD1A) [MIM:159000]. LGMD1A is an autosomal dominant degenerative myopathy with onset within a mean age of 28 years. LGMD1A is characterized by progressive skeletal muscle weakness of the hip and shoulder girdles, later progressing to include distal weakness, as well as a distinctive dysarthric pattern of speech. Affected muscle exhibits disorganization and streaming of the Z-line.Defects in MYOT are the cause of myopathy myofibrillar myotylin-related (MFM-MYOT) [MIM:609200]. A neuromuscular disorder characterized by progressive skeletal muscle weakness greater distally than proximally, tight heel cords, hyporeflexia, cardiomyopathy and peripheral neuropathy in some patients. Affected muscle exhibits disorganization and streaming of the Z-line, presence of large hyaline structures, excessive accumulation of myotilin and other ectopically expressed proteins and prominent congophilic deposits.Defects in MYOT are the cause of spheroid body myopathy (SBM) [MIM:182920]. SBM is an autosomal dominant form of myofibrillar myopathy (MFM), characterized by slowly progressing proximal muscle weakness and dysarthric nasal speech. There is no evidence of cardiomyopathy. Muscle biopsy shows spheroid bodies within the type I muscle fibers.